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A260626
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a(n) = gcd(m, 2^m-1) where m is the n-th nonprime positive integer.
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1
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1, 1, 3, 1, 1, 1, 3, 1, 1, 1, 9, 5, 7, 1, 3, 1, 1, 1, 1, 3, 1, 1, 1, 1, 9, 1, 1, 5, 21, 1, 1, 1, 3, 1, 1, 1, 1, 27, 1, 1, 1, 1, 15, 1, 7, 1, 1, 3, 1, 1, 1, 9, 1, 1, 1, 1, 3, 5, 1, 1, 21, 1, 1, 1, 1, 9, 1, 1, 1, 1, 1, 3, 1, 1, 25, 3, 1, 7, 1, 27, 11, 1, 1, 3, 1
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OFFSET
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1,3
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COMMENTS
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2^m - 1 is a nonprime number if m is a nonprime number.
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LINKS
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Michel Lagneau, Table of n, a(n) for n = 1..10000
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FORMULA
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a(n) = gcd(A018252(n), 2^A018252(n)-1).
a(n) = A014491(A018252(n)). - Michel Marcus, Nov 01 2015
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MAPLE
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seq(`if`(isprime(m), NULL, igcd(m, 2^m-1)), m=1..150);
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MATHEMATICA
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GCDnonPrime[n_Integer]:=GCD[2^FixedPoint[n+PrimePi@#&, n+PrimePi@n]-1, FixedPoint[n+PrimePi@#&, n+PrimePi@n]]; Array[GCDnonPrime, 120]
GCD[#, 2^#-1]&/@Select[Range[200], !PrimeQ[#]&] (* Harvey P. Dale, Aug 25 2019 *)
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PROG
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(PARI) for(n=1, 1e3, if(!isprime(n), print1(gcd(n, 2^n-1)", "))) \\ Altug Alkan, Nov 01 2015
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CROSSREFS
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Cf. A014491, A018252.
Sequence in context: A060901 A351545 A087612 * A155828 A226203 A327791
Adjacent sequences: A260623 A260624 A260625 * A260627 A260628 A260629
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KEYWORD
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nonn,easy
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AUTHOR
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Michel Lagneau, Oct 31 2015
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STATUS
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approved
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